Powder composition for castable refractory and premixed material comprising the same, method for applying premixed material and refractory hardene product therefrom

ABSTRACT

A premixed material is obtained by tempering a castable refractory powder composition comprising refractory aggregate, fine refractory powder, alumina cement, a dispersing agent and an alumina cement hydration stopper with water. The hydration stopper is acidic in a state of an aqueous solution. The amount of the hydration stopper is controlled such that the premixed material has a pH of 2 to 7. Immediately after adding and mixing an alumina cement hydration starter to the premixed material, the resultant mixture is cast into a mold. The addition of the hydration starter can be carried out 5 days or more after the production of the premixed material.

FIELD OF THE INVENTION

The present invention relates to a castable refractory powdercomposition usable for linings of vessels for molten metals such astroughs for blast furnaces, ladles, tundishes, etc., a premixed materialprepared therefrom, a method for hardening the premixed material at roomtemperature without heating, and a hardened refractory body obtained bysuch a method.

BACKGROUND OF THE INVENTION

Premixed castable refractories (hereinafter referred to as “premixedmaterials”), which are obtained by tempering castable refractory powdercompositions with water or other tempering liquids in advance in othersites than casting sites, such as factories, etc., and transported tothe casting sites, have recently become widely used as refractories forlinings of vessels for molten metals such as troughs for blast furnaces,ladles, tundishes, etc.

Though the premixed materials suffer from new problems such as hardeningwith time, the separation of aggregate or water during transportation,etc., they are advantageous over conventional castable refractorymaterials in (a) reduced unevenness in the properties of refractorybodies obtained therefrom because of a stabilized amount of temperingwater and sufficient tempering, (b) the omission of a tempering stepleading to reduced labor in site and the generation of no dust,resulting in improved working environment, and (c) no hardening even ifa casting operation is once stopped, because the materials are nothardened at room temperature, etc. Because of these advantages, thepremixed materials have become widely used.

However, attention has recently become paid to the hardening of thematerials again. Because the premixed materials are not hardened at roomtemperature, it is necessary to harden the materials by some means toremove molds after casting. The premixed materials are hardened usuallyby heating via the molds. As such a heat-hardening method, JP 4-83764 Aand JP 6-48845 A disclose methods for thermally hardening premixedmaterials containing heat-hardening agents at a temperature of 80° C. orhigher. However, these heat-hardening methods are disadvantageous inhigh casting cost because of energy loss due to heat-hardening, andperiodic maintenance due to the thermal deformation of molds, etc. Theyare also disadvantageous in the reduced strength of the resultantrefractory body due to rapid water removal by heating.

To solve the problems of these heat-hardening methods, a method ofadding a room-temperature-hardening binder to a premixed materialimmediately before casting, and hardening the material at roomtemperature was newly proposed. For instance, JP 5-60469 A uses aluminacement in the form of slurry as the room-temperature-hardening binder.However, because the alumina cement slurry is hardened with time, itcannot be produced in advance, but should be prepared at the time ofcasting.

On the other hand, JP 2000-16843 A proposes an alumina cementcomposition having an extremely long working time, its gunning methodand an unshaped refractory obtained by such a gunning method. It can bestored and used days after gunning without discarding a castablerefractory remaining in an apparatus because of a extremely long workingtime. Accordingly, the gunning method using such an alumina cementcomposition enables the reduction of cost and working.

The alumina cement composition of JP 2000-16843 A comprises aluminacement prepared from a clinker having a crystalline mineral compositioncomprising 60 to 95% by weight of CaO.2Al₂O₃, 5 to 30% by weight of2CaO.Al₂O₃.SiO₂ and 10% or less by weight of CaO.Al₂O₃, and a hardeningretarder for the alumina cement. This reference discloses that it ispreferable to use as a retarder at least one selected from the groupconsisting of phosphoric acids, a boric acid, silicofluorides,hydroxycarboxylic acids, polycarboxylic acids, polyhydroxycarboxylicacids, polyoxyalkylenes and saccharides. However, the alumina cementclinker mineral described in this reference comprises CaO.2Al₂O₃ and2CaO.Al₂O₃.SiO₂ as main components, its hydrating activity is extremelylow. Accordingly, though hardening retarders composed of alkaline saltssuch as sodium tripolyphosphate, sodium citrate, sodium polyacrylate,etc., which are described in Examples of this reference, exhibit aneffective retarding effect on the alumina cement based onlow-hydrating-activity clinker minerals, their retarding effect oncommon alumina cement based on high-hydrating-activity CaO.Al₂O₃ is asinsufficient as failing to reach 24 hours.

OBJECT OF THE INVENTION

Accordingly, an object of the present invention is to provide a castablerefractory powder composition containing alumina cement capable ofproviding a premixed material by tempering with water, which can keepflowability for a long period of time.

Another object of the present invention is to provide a premixedmaterial containing alumina cement, which can keep flowability for along period of time.

A further object of the present invention is to provide a method forcasting such a premixed material comprising making it hardenable at roomtemperature at the time of casting.

A still further object of the present invention is to provide a hardenedrefractory body obtained by hardening such a premixed material at roomtemperature.

DISCLOSURE OF THE INVENTION

As a result of intensive research in view of the above object, theinventors have found that (a) the addition of a material for stoppingthe hydration reaction of alumina cement (hereinafter referred to as“hydration stopper”) to a powder composition containing alumina cementfor castable refractories provides a premixed material, which would notbe hardened at room temperature for a necessary period of time evenafter tempering with water, and that (b) the mixing of the abovepremixed material with a material for recovering hydratability bybreaking the hydration-stopping mechanism of alumina cement (hereinafterreferred to as “hydration starter”) makes the premixed materialhardenable at room temperature. The present invention has been completedbased on these findings.

Thus, the castable refractory powder composition of the presentinvention comprises refractory aggregate, fine refractory powder,alumina cement, a dispersing agent and a powdery hydration stopper forthe alumina cement, the hydration stopper being a material, which isacidic in a state of an aqueous solution, and the amount of thehydration stopper being controlled such that a premixed materialobtained by tempering the castable refractory powder composition withwater has a pH of 2 to 7.

The premixed material of the present invention is obtained by temperinga castable refractory powder composition comprising refractoryaggregate, fine refractory powder, alumina cement, a dispersing agentand a hydration stopper for the alumina cement with water in advance,the hydration stopper being a material, which is acidic in a state of anaqueous solution, and the amount of the hydration stopper beingcontrolled such that the premixed material has a pH of 2 to 7.

The method of the present invention for casting a premixed materialcomprises tempering a castable refractory powder composition comprisingrefractory aggregate, fine refractory powder, alumina cement, adispersing agent and an alumina cement hydration stopper with water inadvance to prepare the premixed material, adding an alumina cementhydration starter to the premixed material and mixing them immediatelybefore casting, and then casting the resultant mixture into a mold. Itis preferable that a material, which is acidic in a state of an aqueoussolution, is used as the hydration stopper, that the amount of thehydration stopper is controlled such that the premixed material has a pHof 2 to 7, and that the amount of the hydration starter is preferably0.02 to 0.5% by mass (outer percentage), based on the total amount (100%by mass) of the refractory aggregate, the fine refractory powder and thealumina cement.

The hardened refractory body of the present invention is obtained byadding an alumina cement hydration starter to the above premixedmaterial and mixing them, and then casting the resultant mixture.

The hydration stopper used in the castable refractory powder compositionis preferably at least one selected from the group consisting ofhydroxycarboxylic acids and their salts, a polyacrylic acid and itsderivatives, salts of an acrylic acid, chelating agents, condensedphosphate, aluminum phosphate and a boric acid. When used in thepremixed material, a phosphoric acid may be used as the hydrationstopper in place of the above compounds.

The alumina cement hydration starter added to the premixed material ispreferably at least one selected from the group consisting ofaluminates, hydroxides, carbonates, nitrites, silicates and borates ofalkali metals, and oxides and hydroxides of alkaline earth metals.

In the casting method of the present invention, it is preferable toconvey the premixed material through a pipe by the action of a pump, addthe alumina cement hydration starter to the premixed material in thepipe and mix them by a line mixer connected to the pipe, and cast theresultant mixture from the outlet into the mold.

The storable days of the premixed material of the present inventionafter production (days during which the premixed material retainscastable flowability) are 5 days or more, preferably 7 days or more.Accordingly, there may be 5 days or more, preferably 7 days or more fromthe production of the premixed material to the addition of the hydrationstarter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a partial cross-sectional view showing one example of anapparatus for casting the premixed material of the present invention,which comprises a line mixer having an outlet at one end; and

FIG. 1(b) is a partial cross-sectional view showing another example ofan apparatus for casting the premixed material of the present invention,which comprises a line mixer and a flexible hose connected to a tip endthereof.

THE BEST MODE FOR CARRYING OUT THE INVENTION

[1] Castable Refractory Powder Composition and Premixed Material

The castable refractory powder composition of the present inventioncomprises refractory aggregate, fine refractory powder, alumina cement,a dispersing agent and a small amount of powdery alumina cementhydration stopper. The castable refractory powder composition mayproperly comprise thickeners, reinforcing materials, agents forpreventing explosive spalling, antioxidants, etc., if necessary, inaddition to the above components. The premixed material of the presentinvention is prepared by tempering the above-described castablerefractory powder composition with water to castable flowability inadvance.

(A) Alumina Cement

The alumina cement of JIS Class 1, 2 or 3 is preferably used in thepresent invention to provide the resultant cast refractories with fireresistance, corrosion resistance and high-temperature strength, etc. Theamount of the alumina cement depends on the type of the hydrationstopper.

The amount of the alumina cement is preferably 0.1 to 12% by mass basedon the total amount (100% by mass) of the refractory aggregate, the finerefractory powder and the alumina cement. When the amount of the aluminacement is less than 0.1% by mass, the resultant hardened refractory bodydoes not have sufficient strength when a mold is removed. On the otherhand, when it exceeds 12% by mass, the premixed material has poorstorability, resulting in a deteriorated corrosion resistance. Theamount of the alumina cement is more preferably 0.3 to 8% by mass.

(B) Hydration Stopper

The hydration stopper is a material, whose aqueous solution is acidic.When the castable refractory powder composition per se is merchandized,the hydration stopper should be powdery. Preferable examples of thepowdery hydration stopper include hydroxycarboxylic acids and theirsalts, a polyacrylic acid and its derivatives, salts of an acrylic acid,chelating agents, condensed phosphate, aluminum phosphate and a boricacid, which may be used alone or in combination. On the other hand, whenthe premixed material is merchandised, the hydration stopper needs notbe in a powdery state but may be phosphoric acid usually sold in awater-containing state.

Specific examples of the hydroxycarboxylic acid or its salt includeglycolic acid, lactic acid, citric acid, sodium dihydrogen citrate,tartaric acid, malic acid, malonic acid, gluconic acid, basic aluminumlactate [for instance, “TAKICERAM GM” (trade name) containing 32% bymass of Al₂O₃, 45.5% by mass of lactic acid and 4.8% by mass of P₂O₅,available from Taki Chemical Co., Ltd.], etc. Because lactic acid andgluconic acid are liquids, they are added to the premixed material.

The polyacrylic acid derivatives are copolymers of an acrylic acidmonomer and another monomer. Another monomer is selected from thosehaving no adverse effect on the solubility of the polymers in water. Thesalts of an acrylic acid may be aluminum acrylate, etc. The chelatingagents may be EDTA, etc. Examples of the condensed phosphate includeacidic sodium pyrophosphate, sodium hexametaphosphate, acidic sodiumhexametaphosphate, sodium ultrapolyphosphate, etc.

Among the hydration stoppers usable in the present invention, condensedphosphate and a polyacrylic acid may also be used as a dispersing agent.However, the amount of condensed phosphate or a polyacrylic acid addedas the dispersing agent is usually about 0.05 to 0.15% by mass, toosmall to make the premixed material have a pH of 2 to 7. For instance,in the case of sodium ultrapolyphosphate, as described in Example 8below, the amount of sodium ultrapolyphosphate added is preferably 0.4%by mass. The inventors have unexpectedly found that condensed phosphateand a polyacrylic acid acting as the dispersing agent when added in asmall amount would be able to stop the hydration reaction of the aluminacement, making it possible to store the premixed material for 5 days ormore, if they were added in such an increased amount as to make thepremixed material have a pH of 2 to 7.

Accordingly, the amount of the acidic hydration stopper should beadjusted to make the premixed material have a pH of 2 to 7, though itmay mainly depend on the acidity of the hydration stopper and the amountof the alumina cement in the castable refractory powder composition.When the premixed material has a pH of higher than 7, thehydration-stopping effect is too small to have high storability. On theother hand, when the premixed material has a pH of lower than 2, thepremixed material is likely to be false setted, similarly failing tohave high storability. It is presumed that considerable heat generationin this false setting phenomenon is caused by a direct chemical reactionbetween the alumina cement and the acid. The premixed materialpreferably has a pH of 3 to 6.

It is presumed that the acidic hydration stopper functions according tothe following mechanism. When brought into contact with water, thealumina cement is immediately reacted to elute Ca²⁺ and Al³⁺ ions. As aresult, the pH of water increases, and a hydrate of alumina cementstarts to be deposited when the pH reaches a certain level. However, theexistence of the acidic hydration stopper captures Ca²⁺, so that theadded water kept slightly acidic functions to suppress the hydrationreaction of alumina cement. In addition, the gelation of aluminumhydroxide, one of alumina cement hydrates, occurs. This aluminumhydroxide gel is deposited on and covers a surface of the aluminacement. It is presumed that though the amount of the aluminum hydroxidegel formed is small, the aluminum hydroxide gel stably exists on thesurface of the alumina cement in a state where the added water is keptacidic, so that the hydration reaction of the alumina cement stops. Ofcourse, this presumption concerning the hydration-stopping mechanismdoes not restrict the scope of the present invention.

The hydration reaction of the premixed material of the present inventioncontaining the hydration stopper stops at least for 5 days afterproduction, preferably for 7 days or more. As a result, the storabledays of the premixed material (days during which it has castableflowability) are 5 days or more, preferably 7 days or more. Accordingly,there are sufficient days from production in a factory to storing,transportation to a casting site and casting at the site.

(C) Refractory Aggregate and Fine Refractory Powder

Usable as the refractory aggregate is at least one selected from thegroup consisting of electrofused alumina, sintered alumina, bauxite,kyanite, andalusite, mullite, chamotte, pyrophyllite, quartz,alumina-magnesia spinel, magnesia, zircon, zirconia, silicon carbide,graphite, pitch, etc., and two or more of them may be used incombination, if necessary. Usable as the fine refractory powder is finepowder of at least one selected from the group consisting of alumina,amorphous silica, silica, titania, mullite, zirconia, chromia, siliconcarbide, carbon, clay, etc. The fine refractory powder preferably has anaverage size of 70 μm or less. The use of ultrafine refractory powder assmall as 10 μm or less, preferably 1 μm or less as part of the finerefractory powder provides a premixed material with good flowabilityeven with a reduced amount of water, when used with a dispersing agent.

(D) Dispersing Agent

Preferable examples of the dispersing agent include sodiumhexametaphosphate, acid sodium hexametaphosphate, condensed phosphatesuch as sodium ultrapolyphosphate, etc., P-naphthalenesulfonate-formalincondensates, melamine sulfonate-formalin condensates, an aluminosulfateand its salts, a lignin sulfonic acid and its salts, a polyacrylic acidand its salts, and polycarboxylic acids and their salts, etc., and theymay be used alone or in combination.

The amount of the dispersing agent is preferably 0.01 to 1% by mass(outer percentage) based on the total amount (100% by mass) of therefractory aggregate, the fine refractory powder and the alumina cement.When the amount of the dispersing agent is less than 0.01% by mass ormore than 1% by mass, it is difficult to obtain a good dispersion of thefine refractory powder. Because all dispersing agents may notnecessarily be added in the above range, the amount should be properlychanged depending on the type of the dispersing agent. For instance,when condensed phosphate and a polyacrylic acid and its salts are used,their amount is usually about 0.05 to 0.15% by mass.

(E) Other Components

In addition to the above components, the castable refractory powdercomposition of the present invention may contain other components in arange (outer percentage), in which the storability of the premixedmaterial and the function of the hydration starter are not hindered. Forinstance, it may contain inorganic or metal fibers for improving thestrength of the cast body, organic fibers or foaming agents forpreventing steam explosion during drying, antioxidants such as boroncarbide, etc. The premixed material of the present invention may furthercontain thickeners such as cellulose derivatives, gums, alginates, etc.,for preventing the separation of the aggregate or water duringtransportation.

(F) Amount of Tempering Water

The premixed material of the present invention is controlled to havecastable workability by tempering the above castable refractory powdercomposition with water in advance, and the amount of the tempering wateris an important factor to obtain a dense refractory body. The density ofthe refractory body can be increased by uniformly tempering the castablerefractory powder composition with the tempering water in such a reducedamount that the flowability is not deteriorated. Though greatly affectedby the specific gravity and porosity of refractory aggregate and finerefractory powder used, the particle size distribution of a refractorycomposition, other components, etc., the amount of the tempering wateris preferably about 4.5 to 9% by mass (outer percentage), and morepreferably 5 to 8.5% by mass (outer percentage), based on 100% by massof the castable refractory powder composition. When the amount of thetempering water is less than 4.5% by mass, the resultant premixedmaterial has low flowability. On the other hand, when it exceeds 9% bymass, the separation of the aggregate and water from the premixedmaterial tends to occur during transportation.

[2] Hydration Starter

The hydration starter is a material for recovering the stopped hydrationof the alumina cement. Usable as the hydration starter is at least oneselected from the group consisting of aluminates, hydroxides,carbonates, nitrites, silicates and borates of alkali metals, and oxidesand hydroxides of alkaline earth metals. The type and amount of thehydration starter should be determined depending on the type and amountof the hydration stopper added to the premixed material.

The amount of the hydration starter added is preferably 0.02 to 0.5% bymass (outer percentage) based on the total amount (100% by mass) of therefractory aggregate, the fine refractory powder and the alumina cement.When two or more hydration starters are used in combination, their totalamount is preferably 0.02 to 0.5% by mass (outer percentage). When it isless than 0.02% by mass, sufficient strength is not obtained. When itexceeds 0.5% by mass, the false setting of the material occurs,resulting in difficulty in casting. The amount of the hydration starteris more preferably 0.04 to 0.3% by mass (outer percentage). Thehydration starter may be added in the form of a solution or slurry.

It is presumed that the hydration starter functions according to thefollowing mechanism. When added to the premixed material, the hydrationstarter turns water in the premixed material alkaline because it isalkaline. Alkaline water dissolves a film of an aluminum hydroxide gelcovering the surface of the alumina cement, exposing an unreacted newsurface of the alumina cement, thereby starting the hydration reactionof the alumina cement.

[3] Casting Method

The method for casting the premixed material of the present inventioncomprises adding the alumina cement hydration starter to the premixedmaterial and mixing them immediately before casting, and then castingthe resultant mixture into a mold. A means for adding the alumina cementhydration starter to the premixed material and mixing them is notrestrictive, but may be a usual mixer or other means. However, it ispreferable to use a line mixer as a mixing means, to make in-site mixingunnecessary as one of the advantages of the premixed material, and tosave labor in a mixing step.

The line mixer is an apparatus having no driving means but a mechanismof disturbing a fluid flow by the energy of an entering fluid.Accordingly, the line mixer in a piping system uniformly mixes a fluid(for instance, different liquids, powder or these mixtures). Usable asthe line mixer are a static mixer, a twisted pipe, combineddifferent-size pipes, etc., and the static mixer is preferable inexcellent stirring capacity.

The static mixer is a tubular apparatus having spiral mixing elementsmounted therein, so that two or more fluids passing through the pipe canbe uniformly mixed. Thus, the static mixer may be called “stationarymixer.” A preferred example of the static mixer is disclosed in JP2000-356475 A. Particularly preferable is a static mixer comprising 6 ormore mixing elements of 40 to 150 mm in inner diameter with an axiallength/inner diameter ratio of 1.5 to 3.

Referring to FIG. 1(a), an example of the casting method using the linemixer is explained below. The depicted casting apparatus comprises apipe 5, a pump 3 disposed upstream of the pipe 5, a hopper 4 mounted tothe pump 3, a line mixer 9 having an outlet 10 attached to thedownstream end of the pipe 5 via a hydration-starter-injecting means 8,a metering pump 6 disposed upstream of the pipe 18 connected to thehydration-starter-injecting means 8, and a vessel 7 disposed upstream ofthe pump 6 for storing an aqueous solution or slurry 17 of the hydrationstarter.

The castable refractory powder composition containing a small amount ofan alumina cement hydration stopper is first tempered with water to havecastable workability in advance in a different site than a casting site,such as a production factory, etc. The resultant premixed material 1 isstored in a plastic container bag 2, etc., such that water is notevaporated, and transported to a casting site on demand. In the castingoperation, the premixed material 1 is charged into the hopper 4, andconveyed to the outlet 10 through the pipe 5 by the action of the pump3. During conveying, the aqueous solution or slurry 17 of the hydrationstarter is injected from the hydration-starter-injecting means 8 intothe pipe 5 by the action of the metering pump 6. While passing throughthe line mixer 9, the aqueous solution or slurry 17 of the hydrationstarter is uniformly mixed with the premixed material 1 to form aroom-temperature-hardenable premixed material 11. Theroom-temperature-hardenable premixed material 11 is cast from the outlet10 into a mold 13 (in the depicted example, space between a permanentlining 12 for a molten metal and the mold 13).

Thought not particularly restricted, the pump 3 used in the presentinvention is preferably a piston type or a squeeze type. As long as theaqueous solution or slurry 17 of the hydration starter can be introducedinto the premixed material 1 conveyed through the pipe 5 under pressure,the hydration-starter-injecting means 8 is not particularly restricted.It may be, for instance, a so-called dry-gunning nozzle body with a ringtherein uniformly having about 8 to 16 apertures or slits forintroducing water, which is connected to a nozzle. The metering pump 6used for introducing the aqueous solution or slurry 17 of the hydrationstarter into the pipe 5 is preferably a multiple non-pulsating plungerpump or mohno (NEMO®) pump, more preferably a multiple non-pulsatingplunger pump capable of conducting high-pressure injection. Theinjection pressure of the metering pump 6 is preferably 5 kgf/cm² ormore.

Though the line mixer 9 is adjacent to the hydration-starter-injectingmeans 8 in the example shown in FIG. 1, the position of the line mixer 9may be properly changed. For instance, part of the pipe 5 may extendbetween the line mixer 9 and the hydration-starter-injecting means 8.Though one end of the line mixer 9 serves as an outlet 10 in the exampleshown in FIG. 1(a), a flexible hose 14 made of rubber, etc., may beconnected to the line mixer 9 as shown in FIG. 1(b) for easy handling,when a casting site is narrow and congested, or when a casting site islocated at such a high position that the arrangement of the pipe isrestricted.

The present invention will be explained in more detail referring toExamples below without intention of restricting the scope of the presentinvention.

REFERENCE EXAMPLE 1

With respect to aqueous solutions of various hydration stoppers foralumina cement, the measurement results of their pH are shown inTable 1. The concentrations of the hydration stoppers whose pH wasmeasured are as follows. For comparison, the pH of trisodium citrate isalso shown. TABLE 1 Hydration Stopper pH Citric Acid 1.8⁽¹⁾ SodiumDihydrogen Citrate 3.6⁽¹⁾ Basic Aluminum Lactate 4.6⁽¹⁾ (TAKICERAM GM)Tartaric Acid 1.6⁽¹⁾ Polyacrylic Acid 2.1⁽¹⁾ Chelating Agent EDTA 4.3⁽¹⁾Sodium Hexametaphosphate 6.0⁽¹⁾ Acidic Sodium Hexametaphosphate 1.3⁽¹⁾Sodium Ultrapolyphosphate 1.4⁽¹⁾ Phosphoric Acid 0.9⁽²⁾ AluminumPhosphate 1.4⁽³⁾ Boric Acid 4.3⁽¹⁾ Trisodium Citrate 8.2⁽¹⁾Note:⁽¹⁾pH was measured on 5 g of powder in 100 cm³ of water.⁽²⁾pH was measured on 5 cm³ of a phosphoric acid solution (solidconcentration: 85% by mass) in 95 cm³ of water.⁽³⁾pH was measured on 5 cm³ of an aluminum phosphate solution (solidconcentration: 73% by mass) in 95 cm³ of water

EXAMPLES 1 TO 9, COMPARATIVE EXAMPLES 1 TO 3

Various hydration stoppers shown in Table 1 were added to a castablerefractory powder composition having a formulation shown in Table 2, andthe resultant composition was tempered with 6.5% by mass (outerpercentage) of water in a utility mixer to prepare a premixed material.The resultant premixed material was stored at 25±1° C. The relationsbetween the pH and storability of the resultant premixed materials areshown in Table 3. TABLE 2 Formulation Components (% by mass) RefractoryAggregate Electrofused Alumina (Particle Size: 8 to 5 mm) 7 ElectrofusedSpinel (Particle Size: 5 to 1 mm) 34 Electrofused Alumina (ParticleSize: 1 mm or less) 24 Fine Refractory Powder Electrofused Alumina(Particle Size: 200 μm or less) 7 Silicon Carbide (Particle Size: 200 μmor less) 15 Calcined Alumina (Particle Size: 10 μm or less) 7 CarbonBlack (Particle Size: 1 μm or less) 1 Amorphous Silica (Particle Size: 1μm or less) 2 Pitch 1 Alumina Cement (JIS Class 1) 2 Dispersing Agentβ-Naphthalenesulfonate-Formalin Condensate 0.1⁽¹⁾ Other componentsPolypropylene fibers 0.07⁽¹⁾ Carboxymethylcellulose 0.02⁽¹⁾ Amount⁽²⁾ ofTempering Water 6.5⁽¹⁾Note:(1) Outer percentage.(2) Based on 100% by mass of the castable refractory powder composition.

TABLE 3 No. Example 1 Example 2 Example 3 Example 4 Hydration BasicCitric Tartaric EDTA Stopper 1 Aluminum Acid Acid (0.7%) (% by mass)Lactate (0.5%) (0.2%) (1%) Hydration Sodium — — — Stopper 2 Hexameta- (%by mass) phosphate (0.3%) Amount⁽¹⁾ of 6.5 6.5 6.5 6.5 Tempering Waterph⁽²⁾ of 5 to 6 4 4 5 to 6 Premixed Material Storable 7< 7< 7< 7< Daysat 25° C. No. Example 5 Example 6 Example 7 Example 8 HydrationPhosphoric Aluminum Polyacrylic Sodium Stopper 1 Acid Phosphate Acid(0.8%) Ultrapoly- (% by mass) (0.05%) (0.1%) phosphate (0.4%) Hydration— — — — Stopper 2 (% by mass) Amount⁽¹⁾ of 6.5 6.5 6.5 6.5 TemperingWater ph⁽²⁾ of 5 4 4 4 Premixed Material Storable 7< 7< 7< 7< Days at25° C. Comparative Comparative Comparative No. Example 9 Example 1Example 2 Example 3 Hydration Sodium Sodium Trisodium Phosphoric Stopper1 Hexameta- Hexameta- Citrate Acid (% by mass) phosphate phosphate(0.8%) (0.15%) (0.3%) (0.1%) Hydration Boric Acid Boric Acid — — Stopper2 (0.2%) (0.1%) (% by mass) Amount⁽¹⁾ of 6.5 6.5 6.5 6.5 Tempering Waterph⁽²⁾ of 5 to 6 8 12 1 Premixed Material Storable 7< 1> 1> 1> Days at25° C.Note:⁽¹⁾Outer percentage.⁽²⁾Measured on a day when it was produced.

In Examples 1 to 9, basic aluminum lactate (TAKICERAM GM)+sodiumhexametaphosphate, citric acid, tartaric acid, a chelating agent (EDTA),phosphoric acid, aluminum phosphate, polyacrylic acid, sodiumultrapolyphosphate, or sodium hexametaphosphate+boric acid were added asa hydration stopper to the castable refractory powder composition. Inany Examples, the pH of the premixed material could be controlled within2 to 7 on a day when they were produced. Any of these premixed materialshad a storable day of 1 week or more.

On the contrary, in Comparative Example 1 using the same hydrationstopper (sodium hexametaphosphate+boric acid) as in Example 9, theresultant premixed material had as high pH as 8 because the hydrationstopper was added in an insufficient amount. In Comparative Example 2using trisodium citrate as alkaline as pH 8.2, improper as the hydrationstopper, the resultant premixed material had as extremely high pH as 12.As a result, in both Comparative Examples 1 and 2, the storable days ofthe premixed materials were as short as less than one day. InComparative Example 3 using phosphoric acid as the hydration stopper,the resultant premixed material had as low pH as less than 2. It is thushighly likely that an acid-base reaction occurred directly betweenphosphoric acid and alumina cement, resulting in false setting with heatgeneration in a short period of time.

EXAMPLES 10 TO 23, AND COMPARATIVE EXAMPLES 4 AND 5

Various hydration starters were added to the premixed materials ofExamples 1 to 9, to investigate the hardening speed of the premixedmaterial hardened by each hydration starter at room temperature. Thecastable refractory powder compositions containing various hydrationstoppers were tempered with 6.5% by mass (outer percentage) of water ina utility mixer to produce premixed materials. After the resultantpremixed materials were stored at 25±1° C. for 2 days, they were mixedwith various hydration starters, cast into a mold and hardened tomeasure their hardening time. The hardening time was a time period, inwhich no deformation occurred in each hardened body by pressing by afinger. The results are shown in Table 4. TABLE 4 No. Example ExampleExample Example 10 11 12 13 Premixed Material Example 2 Example 3Example 4 Example 5 Hydration Starter Type Sodium Calcium Sodium CalciumAluminate Hydroxide Hydroxide Hydroxide Solution Slurry Solution SlurryConcentration 19 10 25 10 (% by mass) Amount 1.0 0.5 0.5 0.5 (% by mass)Concentration 0.19 0.05 0.125 0.05 (% by mass) on Solid Basis HardeningTime 14 6 3 7 (hours) at 25° C. No. Example Example Example Example 1415 16 17 Premixed Material Example 6 Example 7 Example 8 Example 9Hydration Starter Type Calcium Sodium Sodium Calcium Hydroxide SilicateSilicate Hydroxide Slurry Solution Solution Slurry Concentration 10 2525 10 (% by mass) Amount 0.5 0.5 0.5 0.5 (% by mass) Concentration 0.050.125 0.125 0.05 (% by mass) on Solid Basis Hardening Time 8 6 7 3(hours) at 25° C. No. Example Example Example Example 18 19 20 21Premixed Material Example 3 Example 9 Example 9 Example 3 HydrationStarter Type Sodium Lithium Lithium Sodium Hydroxide Carbonate NitriteSilicate Solution Slurry Slurry Solution Concentration 25 10 10 25 (% bymass) Amount 0.5 0.5 0.5 0.5 (% by mass) Concentration 0.125 0.05 0.050.125 (% by mass) on Solid Basis Hardening Time 4 19 22 5 (hours) at 25°C. No. Compara- Compara- Example Example tive tive 22 23 Example 4Example 5 Premixed Material Example 9 Example 8 Example 8 Example 9Hydration Starter Type Borax Calcium Lithium Calcium Slurry HydroxideCarbonate Hydroxide Slurry Slurry Slurry Concentration 10 10 10 25 (% bymass) Amount 0.5 0.5 0.1 0.5 (% by mass) Concentration 0.05 0.05 0.010.125 (% by mass) on Solid Basis Hardening Time 22 7 ≧2 days False(hours) at 25° C. Setting

All of the premixed materials of Examples 10 to 23 had a hardening timeof within one day, which is required by usual furnace operation. On theother hand, the premixed material of Comparative Example 4 was nothardened even after 2 days because of an insufficient amount of thehydration starter (lithium carbonate), while the premixed material ofComparative Example 5 was immediately subjected to false setting becauseof excessive calcium hydroxide.

EXAMPLE 24

The castable refractory powder composition having the formulation ofExample 1 shown in Table 3 was tempered with 6.5% by mass of water in alarge-vortex mixer, to produce 20 tons of a premixed material. After theresultant premixed material was stored at room temperature (about 15 to23° C.) for 9 days, it was conveyed to a casting site in a steel works,and cast into a large trough of a blast furnace.

Using the casting apparatus shown in FIG. 1(a), the premixed materialwas cast. The specification of the casting apparatus is shown in Table5. TABLE 5 Parts Specification Pump 3 Double-piston pump (maximumejection pressure: 25 MPa) Pipe 5 Steel pipe of 100 mm in inner diameterand 30 m in length Hydration- Improved nozzle body with ring having 16apertures therein Stopper- Injecting Means 8 Metering Triplenon-pulsating plunger pump Pump 6 Flow rate: 0.5 to 33 L/min, Maximumejection ressure: 10 MPa Line Static mixer having two mixing elementstwisting by 180° Mixer 9 clockwise and counterclockwise, respectively,with their ends perpendicular to each other Number of mixing elements:6, Inner diameter: 100 mm, Longitudinal length: 200 mm, and Material:stainless steel.

The premixed material 1 was first introduced into a hopper 4, andconveyed under pressure through a pipe 5 by the action of a pump 3 to ahydration-starter-injecting means 8 disposed near a line mixer 9, atwhich 0.19% by mass (on a solid basis, and outer percentage) of asolution of sodium aluminate (concentration: 19% by mass) was introducedinto the premixed material. The premixed material 1 was mixed throughthe line mixer 9 to obtain a room-temperature-hardenable premixedmaterial 11, which was cast through a nozzle 10 into a cavity between apermanent lining 12 and a mold 13. The room-temperature-hardenablepremixed material 11 was cast into a separate small test mold, andhardened for about 11 hours to form a refractory body. After drying thisrefractory body at 110° C., its properties were measured. The resultsare shown in Table 6. TABLE 6 Bulk Density 2.82 Bending Strength (MPa)1.2 Compression Strength (MPa) 8.2

Though the premixed material produced in a factory distant from acasting site was transported to the casting site, where the premixedmaterial was mixed with a hydration starter and then cast, in the aboveExample, the present invention is not restricted to such method. Forinstance, the castable refractory powder composition may be transportedto a casting site, where it is tempered with a predetermined amount ofwater to produce a premixed material for casting.

Because the premixed material of the present invention makes it possibleto add and mix a hydration starter at a casting site, there is enoughcastable time, resulting in easy casting operation.

As described in detail above, because the premixed material obtained byadding an alumina cement hydration stopper to a castable refractorypowder composition containing alumina cement is not hardened for a longperiod of time, having an extremely long working time, it may reside ina mixer or a tank, etc., for a long period of time. At the time ofcasting, a necessary amount of the premixed material may be mixed with ahydration starter for alumina cement, and then cast into a mold.Accordingly, a premixed material produced in advance is not wasted,providing enough time for a casting operation.

As a result, there is no necessity for heat hardening for removing amold from a refractory body, which is carried out in using conventionalpremixed materials, and thus the periodic maintenance of a moldthermally deformed by the heat hardening may be omitted, resulting indrastic reduction of energy and casting cost.

The refractory body formed by the premixed material of the presentinvention is free from decrease in structural strength, which is causedby rapid dehydration by heating. The use of a line mixer for adding thehydration starter to the premixed material and mixing them enablesfurther saving of work.

1-16. (canceled)
 17. A castable refractory powder composition, which isto be tempered with water to obtain a premixed material hardenable byadding a hydration starter, comprising refractory aggregate, finerefractory powder, alumina cement, a dispersing agent and a powderyhydration stopper for said alumina cement, said hydration stopper beinga material, which is acidic in a state of an aqueous solution, and theamount of said hydration stopper being controlled such that a premixedmaterial has a pH of 2 to
 7. 18. The castable refractory powdercomposition according to claim 17, wherein said hydration stopper is atleast one selected from the group consisting of hydroxycarboxylic acidsand their salts, a polyacrylic acid and its derivatives, salts of anacrylic acid, chelating agents, condensed phosphate, aluminum phosphateand a boric acid.
 19. The castable refractory powder compositionaccording to claim 17, wherein said alumina cement is 0.1 to 12% bymass, and said dispersing agent is 0.01 to 1% by mass (outerpercentage), based on the total amount (100% by mass) of said refractoryaggregate, said fine refractory powder and said alumina cement.
 20. Apremixed material hardenable by adding a hydration starter, saidpremixed material being obtained by tempering a castable refractorypowder composition comprising refractory aggregate, fine refractorypowder, alumina cement, a dispersing agent and a hydration stopper forsaid alumina cement with water in advance, said hydration stopper beinga material, which is acidic in a state of an aqueous solution, and theamount of said hydration stopper being controlled such that saidpremixed material has a pH of 2 to
 7. 21. The premixed materialaccording to claim 20, wherein said hydration stopper is at least oneselected from the group consisting of hydroxycarboxylic acids and theirsalts, a polyacrylic acid and its derivatives, salts of an acrylic acid,chelating agents, condensed phosphate, a phosphoric acid, aluminumphosphate and a boric acid.
 22. The premixed material according to claim20, wherein said castable refractory powder composition comprises 0.1 to12% by mass of said alumina cement and 0.01 to 1% by mass (outerpercentage) of said dispersing agent, based on the total amount (100% bymass) of said refractory aggregate, said fine refractory powder and saidalumina cement.
 23. The premixed material according to claim 20, whereinit can be stored for 5 days or more after production.
 24. A method forcasting a premixed material comprising tempering a castable refractorypowder composition comprising refractory aggregate, fine refractorypowder, alumina cement, a dispersing agent and an alumina cementhydration stopper with water in advance to prepare said premixedmaterial, adding an alumina cement hydration starter to said premixedmaterial and mixing them immediately before casting, and then castingthe resultant mixture into a mold.
 25. The method for casting a premixedmaterial according to claim 24, wherein a material, which is acidic in astate of an aqueous solution, is used as said hydration stopper; whereinthe amount of said hydration stopper is controlled such that saidpremixed material has a pH of 2 to 7; and wherein the amount of saidhydration starter is 0.02 to 0.5% by mass (outer percentage), based onthe total amount (100% by mass) of said refractory aggregate, said finerefractory powder and said alumina cement.
 26. The method for casting apremixed material according to claim 24, wherein said hydration stopperis at least one selected from the group consisting of hydroxycarboxylicacids and their salts, a polyacrylic acid and its derivatives, salts ofan acrylic acid, chelating agents, condensed phosphate, a phosphoricacid, aluminum phosphate and a boric acid; and wherein said aluminacement hydration starter is at least one selected from the groupconsisting of aluminates, hydroxides, carbonates, nitrites, silicatesand borates of alkali metals, and oxides and hydroxides of alkalineearth metals.
 27. The method for casting a premixed material accordingto claim 24, wherein said castable refractory powder compositioncomprises 0.1 to 12% 10 by mass of said alumina cement and 0.01 to 1% bymass (outer percentage) of said dispersing agent, based on the totalamount (100% by mass) of said refractory aggregate, said fine refractorypowder and said alumina cement.
 28. The method for casting a premixedmaterial according to claim 24, comprising conveying said premixedmaterial through a pipe by the action of a pump, adding said aluminacement hydration starter to said premixed material in said pipe andmixing them by a line mixer connected to said pipe, and then casting theresultant mixture from said outlet into said mold.
 29. The method forcasting a premixed material according to claim 24, wherein the additionof said hydration starter can be carried out 5 days or more after theproduction of said premixed material.
 30. A hardened refractory bodyobtained by adding an alumina cement hydration starter to the premixedmaterial recited in claim 20 and mixing them, and then casting theresultant mixture.
 31. The hardened refractory body according to claim30, obtained by mixing said premixed material with at least one selectedfrom the group consisting of aluminates, hydroxides, carbonates,nitrites, silicates and borates of alkali metals, and oxides andhydroxides of alkaline earth metals as said hydration starter foralumina cement, and then casting the resultant mixture.
 32. The hardenedrefractory body according to claim 30, wherein the amount of a hydrationstarter for said alumina cement is 0.02 to 0.5% by mass (outerpercentage), based on the total amount (100% by mass) of said 5refractory aggregate, said fine refractory powder and said aluminacement.